Reapply "[IR] Move optional data in llvm::Function into a hungoff uselist"

Make personality functions, prefix data, and prologue data hungoff
operands of Function.

This is based on the email thread "[RFC] Clean up the way we store
optional Function data" on llvm-dev.

Thanks to sanjoyd, majnemer, rnk, loladiro, and dexonsmith for feedback!

Includes a fix to scrub value subclass data in dropAllReferences.

Differential Revision: http://reviews.llvm.org/D13829

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256093 91177308-0d34-0410-b5e6-96231b3b80d8

8 files changed, 92 insertions, 168 deletions

diff --git a/include/llvm/IR/Function.h b/include/llvm/IR/Function.h
index 2843cf2cce3..2a983930bf4 100644
--- a/include/llvm/IR/Function.h
+++ b/include/llvm/IR/Function.h
@@ -64,7 +64,7 @@ private:
    * bit 0      : HasLazyArguments
    * bit 1      : HasPrefixData
    * bit 2      : HasPrologueData
-   * bit 3      : [reserved]
+   * bit 3      : HasPersonalityFn
    * bits 4-13  : CallingConvention
    * bits 14-15 : [reserved]
    */
@@ -110,7 +110,7 @@ private:
 public:
   static Function *Create(FunctionType *Ty, LinkageTypes Linkage,
                           const Twine &N = "", Module *M = nullptr) {
-    return new(1) Function(Ty, Linkage, N, M);
+    return new Function(Ty, Linkage, N, M);
   }
 
   ~Function() override;
@@ -118,14 +118,6 @@ public:
   /// \brief Provide fast operand accessors
   DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
 
-  /// \brief Get the personality function associated with this function.
-  bool hasPersonalityFn() const { return getNumOperands() != 0; }
-  Constant *getPersonalityFn() const {
-    assert(hasPersonalityFn());
-    return cast<Constant>(Op<0>());
-  }
-  void setPersonalityFn(Constant *C);
-
   Type *getReturnType() const;           // Return the type of the ret val
   FunctionType *getFunctionType() const; // Return the FunctionType for me
 
@@ -525,17 +517,30 @@ public:
   size_t arg_size() const;
   bool arg_empty() const;
 
+  /// \brief Check whether this function has a personality function.
+  bool hasPersonalityFn() const {
+    return getSubclassDataFromValue() & (1<<3);
+  }
+
+  /// \brief Get the personality function associated with this function.
+  Constant *getPersonalityFn() const;
+  void setPersonalityFn(Constant *Fn);
+
+  /// \brief Check whether this function has prefix data.
   bool hasPrefixData() const {
     return getSubclassDataFromValue() & (1<<1);
   }
 
+  /// \brief Get the prefix data associated with this function.
   Constant *getPrefixData() const;
   void setPrefixData(Constant *PrefixData);
 
+  /// \brief Check whether this function has prologue data.
   bool hasPrologueData() const {
     return getSubclassDataFromValue() & (1<<2);
   }
 
+  /// \brief Get the prologue data associated with this function.
   Constant *getPrologueData() const;
   void setPrologueData(Constant *PrologueData);
 
@@ -630,11 +635,15 @@ public:
   DISubprogram *getSubprogram() const;
 
 private:
+  void allocHungoffUselist();
+  template<int Idx> void setHungoffOperand(Constant *C);
+
   // Shadow Value::setValueSubclassData with a private forwarding method so that
   // subclasses cannot accidentally use it.
   void setValueSubclassData(unsigned short D) {
     Value::setValueSubclassData(D);
   }
+  void setValueSubclassDataBit(unsigned Bit, bool On);
 
   bool hasMetadataHashEntry() const {
     return getGlobalObjectSubClassData() & HasMetadataHashEntryBit;
@@ -647,7 +656,7 @@ private:
 };
 
 template <>
-struct OperandTraits<Function> : public OptionalOperandTraits<Function> {};
+struct OperandTraits<Function> : public HungoffOperandTraits<3> {};
 
 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(Function, Value)
 
diff --git a/include/llvm/IR/User.h b/include/llvm/IR/User.h
index 639dc5c01c8..885ae197d22 100644
--- a/include/llvm/IR/User.h
+++ b/include/llvm/IR/User.h
@@ -170,19 +170,6 @@ public:
     NumUserOperands = NumOps;
   }
 
-  /// Set the number of operands on a Function.
-  ///
-  /// Function always allocates space for a single operands, but
-  /// doesn't always use it.
-  ///
-  /// FIXME: As that the number of operands is used to find the start of
-  /// the allocated memory in operator delete, we need to always think we have
-  /// 1 operand before delete.
-  void setFunctionNumOperands(unsigned NumOps) {
-    assert(NumOps <= 1 && "Function can only have 0 or 1 operands");
-    NumUserOperands = NumOps;
-  }
-
   /// \brief Subclasses with hung off uses need to manage the operand count
   /// themselves.  In these instances, the operand count isn't used to find the
   /// OperandList, so there's no issue in having the operand count change.
diff --git a/lib/Bitcode/Writer/ValueEnumerator.cpp b/lib/Bitcode/Writer/ValueEnumerator.cpp
index 2a9b4490ffb..faf82a7926e 100644
--- a/lib/Bitcode/Writer/ValueEnumerator.cpp
+++ b/lib/Bitcode/Writer/ValueEnumerator.cpp
@@ -87,15 +87,9 @@ static OrderMap orderModule(const Module &M) {
     if (!isa<GlobalValue>(A.getAliasee()))
       orderValue(A.getAliasee(), OM);
   for (const Function &F : M) {
-    if (F.hasPrefixData())
-      if (!isa<GlobalValue>(F.getPrefixData()))
-        orderValue(F.getPrefixData(), OM);
-    if (F.hasPrologueData())
-      if (!isa<GlobalValue>(F.getPrologueData()))
-        orderValue(F.getPrologueData(), OM);
-    if (F.hasPersonalityFn())
-      if (!isa<GlobalValue>(F.getPersonalityFn()))
-        orderValue(F.getPersonalityFn(), OM);
+    for (const Use &U : F.operands())
+      if (!isa<GlobalValue>(U.get()))
+        orderValue(U.get(), OM);
   }
   OM.LastGlobalConstantID = OM.size();
 
@@ -273,12 +267,8 @@ static UseListOrderStack predictUseListOrder(const Module &M) {
   for (const GlobalAlias &A : M.aliases())
     predictValueUseListOrder(A.getAliasee(), nullptr, OM, Stack);
   for (const Function &F : M) {
-    if (F.hasPrefixData())
-      predictValueUseListOrder(F.getPrefixData(), nullptr, OM, Stack);
-    if (F.hasPrologueData())
-      predictValueUseListOrder(F.getPrologueData(), nullptr, OM, Stack);
-    if (F.hasPersonalityFn())
-      predictValueUseListOrder(F.getPersonalityFn(), nullptr, OM, Stack);
+    for (const Use &U : F.operands())
+      predictValueUseListOrder(U.get(), nullptr, OM, Stack);
   }
 
   return Stack;
@@ -321,20 +311,10 @@ ValueEnumerator::ValueEnumerator(const Module &M,
   for (const GlobalAlias &GA : M.aliases())
     EnumerateValue(GA.getAliasee());
 
-  // Enumerate the prefix data constants.
+  // Enumerate any optional Function data.
   for (const Function &F : M)
-    if (F.hasPrefixData())
-      EnumerateValue(F.getPrefixData());
-
-  // Enumerate the prologue data constants.
-  for (const Function &F : M)
-    if (F.hasPrologueData())
-      EnumerateValue(F.getPrologueData());
-
-  // Enumerate the personality functions.
-  for (Module::const_iterator I = M.begin(), E = M.end(); I != E; ++I)
-    if (I->hasPersonalityFn())
-      EnumerateValue(I->getPersonalityFn());
+    for (const Use &U : F.operands())
+      EnumerateValue(U.get());
 
   // Enumerate the metadata type.
   //
diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index 51a0faee81c..124fc56e78f 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -103,17 +103,9 @@ static OrderMap orderModule(const Module *M) {
     orderValue(&A, OM);
   }
   for (const Function &F : *M) {
-    if (F.hasPrefixData())
-      if (!isa<GlobalValue>(F.getPrefixData()))
-        orderValue(F.getPrefixData(), OM);
-
-    if (F.hasPrologueData())
-      if (!isa<GlobalValue>(F.getPrologueData()))
-        orderValue(F.getPrologueData(), OM);
-
-    if (F.hasPersonalityFn())
-      if (!isa<GlobalValue>(F.getPersonalityFn()))
-        orderValue(F.getPersonalityFn(), OM);
+    for (const Use &U : F.operands())
+      if (!isa<GlobalValue>(U.get()))
+        orderValue(U.get(), OM);
 
     orderValue(&F, OM);
 
@@ -263,8 +255,8 @@ static UseListOrderStack predictUseListOrder(const Module *M) {
   for (const GlobalAlias &A : M->aliases())
     predictValueUseListOrder(A.getAliasee(), nullptr, OM, Stack);
   for (const Function &F : *M)
-    if (F.hasPrefixData())
-      predictValueUseListOrder(F.getPrefixData(), nullptr, OM, Stack);
+    for (const Use &U : F.operands())
+      predictValueUseListOrder(U.get(), nullptr, OM, Stack);
 
   return Stack;
 }
diff --git a/lib/IR/Function.cpp b/lib/IR/Function.cpp
index 5e4d2d2054e..b6199b827bb 100644
--- a/lib/IR/Function.cpp
+++ b/lib/IR/Function.cpp
@@ -279,9 +279,6 @@ Function::~Function() {
 
   // Remove the function from the on-the-side GC table.
   clearGC();
-
-  // FIXME: needed by operator delete
-  setFunctionNumOperands(1);
 }
 
 void Function::BuildLazyArguments() const {
@@ -328,14 +325,15 @@ void Function::dropAllReferences() {
   while (!BasicBlocks.empty())
     BasicBlocks.begin()->eraseFromParent();
 
-  // Prefix and prologue data are stored in a side table.
-  setPrefixData(nullptr);
-  setPrologueData(nullptr);
+  // Drop uses of any optional data (real or placeholder).
+  if (getNumOperands()) {
+    User::dropAllReferences();
+    setNumHungOffUseOperands(0);
+    setValueSubclassData(getSubclassDataFromValue() & ~0b1110);
+  }
 
   // Metadata is stored in a side-table.
   clearMetadata();
-
-  setPersonalityFn(nullptr);
 }
 
 void Function::addAttribute(unsigned i, Attribute::AttrKind attr) {
@@ -425,18 +423,12 @@ void Function::copyAttributesFrom(const GlobalValue *Src) {
     setGC(SrcF->getGC());
   else
     clearGC();
+  if (SrcF->hasPersonalityFn())
+    setPersonalityFn(SrcF->getPersonalityFn());
   if (SrcF->hasPrefixData())
     setPrefixData(SrcF->getPrefixData());
-  else
-    setPrefixData(nullptr);
   if (SrcF->hasPrologueData())
     setPrologueData(SrcF->getPrologueData());
-  else
-    setPrologueData(nullptr);
-  if (SrcF->hasPersonalityFn())
-    setPersonalityFn(SrcF->getPersonalityFn());
-  else
-    setPersonalityFn(nullptr);
 }
 
 /// \brief This does the actual lookup of an intrinsic ID which
@@ -944,61 +936,67 @@ bool Function::callsFunctionThatReturnsTwice() const {
   return false;
 }
 
-static Constant *
-getFunctionData(const Function *F,
-                const LLVMContextImpl::FunctionDataMapTy &Map) {
-  const auto &Entry = Map.find(F);
-  assert(Entry != Map.end());
-  return cast<Constant>(Entry->second->getReturnValue());
-}
-
-/// setFunctionData - Set "Map[F] = Data". Return an updated SubclassData value
-/// in which Bit is low iff Data is null.
-static unsigned setFunctionData(Function *F,
-                                LLVMContextImpl::FunctionDataMapTy &Map,
-                                Constant *Data, unsigned SCData, unsigned Bit) {
-  ReturnInst *&Holder = Map[F];
-  if (Data) {
-    if (Holder)
-      Holder->setOperand(0, Data);
-    else
-      Holder = ReturnInst::Create(F->getContext(), Data);
-    return SCData | (1 << Bit);
-  } else {
-    delete Holder;
-    Map.erase(F);
-    return SCData & ~(1 << Bit);
-  }
+Constant *Function::getPersonalityFn() const {
+  assert(hasPersonalityFn() && getNumOperands());
+  return cast<Constant>(Op<0>());
+}
+
+void Function::setPersonalityFn(Constant *Fn) {
+  if (Fn)
+    setHungoffOperand<0>(Fn);
+  setValueSubclassDataBit(3, Fn != nullptr);
 }
 
 Constant *Function::getPrefixData() const {
-  assert(hasPrefixData());
-  return getFunctionData(this, getContext().pImpl->PrefixDataMap);
+  assert(hasPrefixData() && getNumOperands());
+  return cast<Constant>(Op<1>());
 }
 
 void Function::setPrefixData(Constant *PrefixData) {
-  if (!PrefixData && !hasPrefixData())
-    return;
-
-  unsigned SCData = getSubclassDataFromValue();
-  SCData = setFunctionData(this, getContext().pImpl->PrefixDataMap, PrefixData,
-                           SCData, /*Bit=*/1);
-  setValueSubclassData(SCData);
+  if (PrefixData)
+    setHungoffOperand<1>(PrefixData);
+  setValueSubclassDataBit(1, PrefixData != nullptr);
 }
 
 Constant *Function::getPrologueData() const {
-  assert(hasPrologueData());
-  return getFunctionData(this, getContext().pImpl->PrologueDataMap);
+  assert(hasPrologueData() && getNumOperands());
+  return cast<Constant>(Op<2>());
 }
 
 void Function::setPrologueData(Constant *PrologueData) {
-  if (!PrologueData && !hasPrologueData())
+  if (PrologueData)
+    setHungoffOperand<2>(PrologueData);
+  setValueSubclassDataBit(2, PrologueData != nullptr);
+}
+
+void Function::allocHungoffUselist() {
+  // If we've already allocated a uselist, stop here.
+  if (getNumOperands())
     return;
 
-  unsigned SCData = getSubclassDataFromValue();
-  SCData = setFunctionData(this, getContext().pImpl->PrologueDataMap,
-                           PrologueData, SCData, /*Bit=*/2);
-  setValueSubclassData(SCData);
+  allocHungoffUses(3, /*IsPhi=*/ false);
+  setNumHungOffUseOperands(3);
+
+  // Initialize the uselist with placeholder operands to allow traversal.
+  auto *CPN = ConstantPointerNull::get(Type::getInt1PtrTy(getContext(), 0));
+  Op<0>().set(CPN);
+  Op<1>().set(CPN);
+  Op<2>().set(CPN);
+}
+
+template <int Idx>
+void Function::setHungoffOperand(Constant *C) {
+  assert(C && "Cannot set hungoff operand to nullptr");
+  allocHungoffUselist();
+  Op<Idx>().set(C);
+}
+
+void Function::setValueSubclassDataBit(unsigned Bit, bool On) {
+  assert(Bit < 16 && "SubclassData contains only 16 bits");
+  if (On)
+    setValueSubclassData(getSubclassDataFromValue() | (1 << Bit));
+  else
+    setValueSubclassData(getSubclassDataFromValue() & ~(1 << Bit));
 }
 
 void Function::setEntryCount(uint64_t Count) {
@@ -1016,22 +1014,3 @@ Optional<uint64_t> Function::getEntryCount() const {
       }
   return None;
 }
-
-void Function::setPersonalityFn(Constant *C) {
-  if (!C) {
-    if (hasPersonalityFn()) {
-      // Note, the num operands is used to compute the offset of the operand, so
-      // the order here matters.  Clearing the operand then clearing the num
-      // operands ensures we have the correct offset to the operand.
-      Op<0>().set(nullptr);
-      setFunctionNumOperands(0);
-    }
-  } else {
-    // Note, the num operands is used to compute the offset of the operand, so
-    // the order here matters.  We need to set num operands to 1 first so that
-    // we get the correct offset to the first operand when we set it.
-    if (!hasPersonalityFn())
-      setFunctionNumOperands(1);
-    Op<0>().set(C);
-  }
-}
diff --git a/lib/IR/LLVMContextImpl.h b/lib/IR/LLVMContextImpl.h
index ae987e65bcb..a24114d0a0a 100644
--- a/lib/IR/LLVMContextImpl.h
+++ b/lib/IR/LLVMContextImpl.h
@@ -1014,17 +1014,6 @@ public:
   /// instructions in different blocks at the same location.
   DenseMap<std::pair<const char *, unsigned>, unsigned> DiscriminatorTable;
 
-  typedef DenseMap<const Function *, ReturnInst *> FunctionDataMapTy;
-
-  /// \brief Mapping from a function to its prefix data, which is stored as the
-  /// operand of an unparented ReturnInst so that the prefix data has a Use.
-  FunctionDataMapTy PrefixDataMap;
-
-  /// \brief Mapping from a function to its prologue data, which is stored as
-  /// the operand of an unparented ReturnInst so that the prologue data has a
-  /// Use.
-  FunctionDataMapTy PrologueDataMap;
-
   int getOrAddScopeRecordIdxEntry(MDNode *N, int ExistingIdx);
   int getOrAddScopeInlinedAtIdxEntry(MDNode *Scope, MDNode *IA,int ExistingIdx);
 
diff --git a/lib/IR/TypeFinder.cpp b/lib/IR/TypeFinder.cpp
index 2ea0550ba45..b5bdab0865b 100644
--- a/lib/IR/TypeFinder.cpp
+++ b/lib/IR/TypeFinder.cpp
@@ -44,14 +44,8 @@ void TypeFinder::run(const Module &M, bool onlyNamed) {
   for (Module::const_iterator FI = M.begin(), E = M.end(); FI != E; ++FI) {
     incorporateType(FI->getType());
 
-    if (FI->hasPrefixData())
-      incorporateValue(FI->getPrefixData());
-
-    if (FI->hasPrologueData())
-      incorporateValue(FI->getPrologueData());
-
-    if (FI->hasPersonalityFn())
-      incorporateValue(FI->getPersonalityFn());
+    for (const Use &U : FI->operands())
+      incorporateValue(U.get());
 
     // First incorporate the arguments.
     for (Function::const_arg_iterator AI = FI->arg_begin(),
diff --git a/lib/Transforms/IPO/GlobalDCE.cpp b/lib/Transforms/IPO/GlobalDCE.cpp
index 1cc657458d6..9b276ed28e2 100644
--- a/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/lib/Transforms/IPO/GlobalDCE.cpp
@@ -215,14 +215,8 @@ void GlobalDCE::GlobalIsNeeded(GlobalValue *G) {
     // any globals used will be marked as needed.
     Function *F = cast<Function>(G);
 
-    if (F->hasPrefixData())
-      MarkUsedGlobalsAsNeeded(F->getPrefixData());
-
-    if (F->hasPrologueData())
-      MarkUsedGlobalsAsNeeded(F->getPrologueData());
-
-    if (F->hasPersonalityFn())
-      MarkUsedGlobalsAsNeeded(F->getPersonalityFn());
+    for (Use &U : F->operands())
+      MarkUsedGlobalsAsNeeded(cast<Constant>(U.get()));
 
     for (BasicBlock &BB : *F)
       for (Instruction &I : BB)